• Tips for golfing in Java

Since Java 25, it's not necessary to wrap main in a class, so shortest boilerplate is:

void main(String[]a){}
// If the hole doesn't have arguments:
void main(){}

Defining a type with var is often shorter. Note that multiple assignment is not possible with this method.

String s="foo";
// vs
var s="foo";

This can save 1 to 2 characters on char scoring. If you need a large integer constant between 1000 and 65535 (inclusive), it may help to use a char literal instead of a number:

var n=30000;
// vs
var n='田';

This can save a few chars when using large numbers that end in zeros

var n=30000;
// vs
var n=3e4;

If you need a single integer initialized to 0, using a field saves 1 byte:

void main(){for(int i=0;i<10;)IO.println(i++);}
// vs
int i;void main(){for(;i<10;)IO.println(i++);}

Java doesn't allow declaring multiple fields like this at once without explicit initializers.